Department of Chemical Engineering

Background, aim, and scope The high consumption of blood lipid regulators is leading to frequent reports of the occurrence of fibrates in natural streams and wastewater effluents. This paper describes a study undertaken to evaluate the acute toxicity of bezafibrate, clofibric acid, gemfibrozil, and fenofibric acid, a metabolite of fenofibrate whose ecotoxicity has not been previously reported. Materials and methods The bioassays used were based on Vibrio fischeri, Daphnia magna, and Anabaena CPB4337 tests. Anabaena CPB4337 is a novel bioassay based on Anabaena sp. PCC 7120 strain CPB4337 bearing in the chromosome a Tn5 derivative with luxCDABE from the luminescent terrestrial bacterium Photorhabdus luminescens. Results The higher toxicity corresponded to fenofibric acid, with EC 50 as low as 1.72 mg/l for V. fischeri. Gemfibrozil was also toxic for Anabaena sp. with EC 50 of 4.42 mg/l. The study reports the results from toxicity tests using fortified real wastewater samples taken from the effluent of a wastewater treatment plant. The wastewater itself was

Several studies have proven that natural or genetically modified bacteria, such as Pseudomonas putida strain, degrade recalcitrant organic sulfur compounds. However, from a practical point of view, the biodesulfurization (BDS) process has to be performed with really high proportions of organic solvents. In this work, the dibenzothiophene (DBT) was selected as recalcitrant model compound, and hexadecane as model organic solvent. It has been observed that P. putida CECT 5279 was able to desulfurize DBT even in the presence of 50% (v/v) of hexadecane. A concentration of 400 ppm of DBT was converted at a specific rate of generation of desulfurized final product, 2-hydroxybiphenyl (HBP), of 2.3 and 1.5 mg HBP L À1 (g DC L À1 h) À1 for 27% and 50% (v/v) of hexadecane, respectively. Finally, the Haldane kinetic model was used to describe the process evolution. The study is relevant as it has been proven that the strain CECT 5279 is a potential biocatalyst for developing an efficient BDS process.

The toxicity of perfluorinated surfactants perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorobutane sulfonate (PFBS) and PF-656 as well as the sulfosuccinate surfactant docusate sodium has been examined using two bioluminescence inhibition assays based on the marine bacterium Vibrio fischeri and the self-luminescent cyanobacterial recombinant strain Anabaena CPB4337. We also determined multigenerational toxicity towards the growth of the algae Pseudokirchneriella subcapitata.

In order to synthesize hydrophobic fine chemicals biocatalysts can be used in aqueous-organic biphasic systems. This can be achieved by immobilizing the biocatalyst in hydrogel beads, which are surrounded by organic solvents. Thus the hydrophobic products can be extracted continuously into the organic phase.

Two cobalt imidazolate metal-organic frameworks were evaluated as a bactericidal material against the growth of the Gram-negative bacteria Pseudomonas putida and Escherichia coli. Under the most unfavourable conditions, within the exponential growth phase and in the culture media for both microorganisms, the growth inhibition reached over 50% for concentrations of biocidal material in the 5-10 mg L −1 range. The release of metal gives excellent durability with the antibacterial effect persisting after 3 months. Both cobalt-based materials can be prepared with simple, cheap and easily accessible commercial ligands, leading to a more affordable possible future application as antimicrobial materials.

Sphingomonas subarctica T7b was isolated from soil in Toyotomi, Hokkaido, Japan as an organism capable of desulfurizing aromatic hydrocarbons in light gas oil (LGO) through enrichment culture. S. subarctica T7b could grow on mineral salt sulfur-free (MSSF) medium with the n-tetradecane oil phase containing dibenzothiophene (DBT), alkyl dibenzothiophenes (alkyl DBTs) or alkyl benzothiophenes (alkyl BTs) as the sole sulfur source and desulfurize these compounds, but could not utilize the tetradecane as a carbon source. This is the first report of a gram-negative bacterium which can desulfurize 4,6-dibutyl DBT and 4,6-dipentyl DBT. The desulfurized product of DBT produced by this strain was 2-hydroxybiphenyl, as in the case of other DBT-desulfurizing bacteria. S. subarctica T7b could desulfurize LGO and the sulfur content was decreased to 41% within 36 h.

Biodesulfurization reaction must be performed in oil-water emulsions with an aerobic biocatalyst which demands oxygen. Different reactor configurations can be used for this purpose, but the bubble column bio-reactors with internal recirculation loop are usually not used. In the present work, the absorption of oxygen in water-dodecane emulsions was studied in a bubble column bio-reactor with internal recirculation loop, in operative conditions normally used for biodesulfurization. The K L a for oxygen was determined for several organic fractions from 0 to 100%, as well as at different gas flow rates. Estimation of K L a was done according to a fluid dynamic model based on an energy balance which takes into account the energy dissipated at the interfaces and on a mass transfer model based on the fluid dynamic model, the Higbie's penetration theory and Kolmogoroff's theory of isotropic turbulence. Experimental data of mass transfer coefficient were simulated with satisfactory accuracy, and differences were less than 20% for most cases. Mayor deviations were obtained for emulsions with 30 and 70% dodecane fraction. To obtain good agreement, assumptions of higher bubble diameter and slip velocity were done, evincing the effect of surface tension and liquid viscosity on the mass transfer coefficient.

Polycyclic aromatic sulphur heterocyclic (PASH) compounds, such as dibenzothiophene (DBT) and alkylated derivatives are used as model compounds in biodesulfurization processes. The development of these processes is focused on the reduction of the concentration of sulphur in gasoline and gas-oil [D.J. Monticello, Curr. Opin. Biotechnol. 11 (2000) 540], in order to meet European Union and United States directives.

Analytical methodologies employed in biodesulfurization processes have been reviewed; attention is primarily focused on the use of analytical techniques in the identification of degradation products and on the monitoring of degradation processes in which microbial sulphur-specific transformations take place. This is the first review of analytical techniques applied to biodesulfurization processes. Methodologies based on gas chromatography (GC) are the most frequently employed, in tandem with various detectors, mainly with the mass spectrometry (MS) detector, and the flame ionization detector (FID). High performance liquid chromatography (HPLC) coupled with ultra violet (UV) detection has also been widely employed. Different sulphurated compounds are used as model in biodesulphurization processes, naphtothiophene (NTH), benzothiophene (BTH), alkilated BTH, dibenzothiophene (DBT), alkilated DBT and their transformation products has been reviewed. DBT is the most frequently employed.

The alkyl-substituted forms of dibenzothiophene (DBT) are the compounds of sulfur most frequently found in crude oils and hydrotreated fraction of diesel, due to their refractory character. Several published studies show the effectiveness of the GMO Pseudomonas putida CECT5279 for the desulfurization of DBT in resting cell operation mode. The process of biocatalyst production and biodesulfurization kinetics of DBT in resting cell operation mode was previously published, but until this time no one reported the use of this biocatalyst for biodesulfurization of alkyl-derivates of DBT in a commercial fermentor. In this work, we present the results obtained in biodesulfurization reaction of dibenzothiophene (DBT) and 4-methyldibenzothiophene (4mDBT) in resting cell operation mode using P. putida CECT5279. Kinetics parameters and yield of biodesulfurization were evaluated for both compounds added separately or mixed in aqueous or in organic matrix. Results indicate that the aqueous biodesulfurization of DBT occurs at higher velocity that the 4mDBT desulfurization reached the 100% of conversion in the operational condition where the compounds are added separately. In aqueous mix of both compounds, reaction rates are slowly but biodesulfurization yield reached is always 100%. In biphasic system, the rate of disappearance of DBT is higher that the measured for 4mDBT and the yield of biodesulfurization reached is around 50% for DBT and 12% for 4mDBT, where each compound was added separately. The desulfurization of the mix of tiophenes in biphasic reaction media occurs slowly that in aqueous media and the yields of elimination of each compound were reduced at 15% for DBT and 7% for 4mDBT. For this work, analytical methods for DBT and metabolites as well as for 4mDBT were developed using a HPLC-DAD.

The objective of this paper is to present a new class of polylactic acid (PLA) fibers containing cobalt-based metal organic frameworks (MOF). The material used was Co-SIM-1, a cobalt-based substituted imidazolate. Composite mats were prepared by electrospinning PLA with a suspension of polyvinylpyrrolidone-stabilized Co-SIM-1. MOF particles formed aggregate of a small number of primary particles that, after electrospun, became completely embedded inside polymeric fibers. The dispersion of particles was better for lower loadings, for which the relative amount of metal released to culture media was also higher. The antimicrobial activity of composite mats was assessed using SEM images, fluorescence microscopy, direct plate reading of fluorescent stains and plate count of colony forming units among other. The microorganisms used in this study were Pseudomonas putida and Staphylococcus aureus. Fluorescence techniques allowed recording viable and damaged cells directly on mat surface and in the culture media embedding the fibers. The results showed higher sensitivity of S. aureus to cobalt-containing fibers, with a reduction in colony forming units of up to 60% with respect to PLA mats. The results also showed the presence of viable but non-culturable microorganisms, which fail to form colonies but yield a positive signal to viable cell staining. Cobalt-based MOF included in electrospun mats provide antibacterial activity suitable to be used to prepare membranes for various biomedical applications.

The degradation of an aqueous solution of clofibric acid was investigated during catalytic and non-catalytic ozonation. The catalyst, TiO 2 , enhanced the production of hydroxyl radicals from ozone and raised the fraction or clofibric acid degraded by hydroxyl radicals. The rate constant for the reaction of clofibric acid and hydroxyl radicals was not affected by the presence of the catalyst. The toxicity of the oxidation products obtained during the reaction was assessed by means of Vibrio fischeri and Daphnia magna tests in order to evaluate the potential formation of toxic byproducts. The results showed that the ozonation was enhanced by the presence of TiO 2, the clofibric acid being removed completely after 15 min at pH 5. The evolution of dissolved organic carbon, specific ultraviolet absorption at 254 nm and the concentration of carboxylic acids monitored the degradation process. The formation of 4chlorophenol, hydroquinone, 4-chlorocatechol, 2-hydroxyisobutyric acid and three non-aromatic compounds identified as a product of the ring opening reaction was assessed by exact mass measurements performed by liquid chromatography coupled to time-of-flight mass spectrometry (LC-TOF-MS). The bioassays showed a significant increase of toxicity during the initial stages of ozonation following a toxicity pattern closely related to the formation of ring-opening by-products.

We prepared non-woven electrospun polylactic acid (PLA) membranes containing functionalized sepiolite fibrillar particles (5 wt. %). Biocidal activity was achieved by functionalizing sepiolite fibers with Ag (26 wt. %) and Cu (26 wt. %), which were embedded in the fiber surface. Sepiolite particles were negatively charged in all cases, with zeta potential in the range of (-15)-(-37) mV, increasing their negative charge with pH. The membranes were biofouled in a cross-flow filtration device using model biofoulants, cultures of Saccharomyces cerevisiae (pH 4.5) and Pseudomonas putida (pH 7.5), which were pumped across the membrane for 24/48 h. The assessment of active biomass was performed by measuring the concentration of adenosine-5'-triphosphate (ATP) in used membranes. The results showed a significant decrease in the amount of surface ATP for PLA loaded with Ag and Cu functionalized sepiolite. The effect was particularly intense for Ag-sepiolite in contact with Saccharomyces cerevisiae, where the reduction amounted to 85% compared to neat PLA (control). This was attributed to the differences in ion availability as a function of pH and to the presence of chloride ions in solution. Pristine sepiolite (without functionalization) did not show any noticeable effect.

BACKGROUND: An important problem exists for the implementation of biodesulfurization technology of fuels related to the influence of mass transfer on the overall reaction rate and process yield. Pseudomonas putida CECT5279 has been shown to be one of the most promising biocatalysts, but most kinetic studies were done at small scale and their capability for the transformation of alkyl substituted forms (Cx-DBTs) has not yet been reported.

Polycyclic aromatic sulphur heterocyclic (PASH) compounds, such as dibenzothiophene (DBT) and alkylated derivatives are used as model compounds in biodesulfurization processes. The development of these processes is focused on the reduction of the concentration of sulphur in gasoline and gas-oil [D.J. Monticello, Curr. Opin. Biotechnol. 11 (2000) 540], in order to meet European Union and United States directives.

Analytical methodologies employed in biodesulfurization processes have been reviewed; attention is primarily focused on the use of analytical techniques in the identification of degradation products and on the monitoring of degradation processes in which microbial sulphur-specific transformations take place. This is the first review of analytical techniques applied to biodesulfurization processes. Methodologies based on gas chromatography (GC) are the most frequently employed, in tandem with various detectors, mainly with the mass spectrometry (MS) detector, and the flame ionization detector (FID). High performance liquid chromatography (HPLC) coupled with ultra violet (UV) detection has also been widely employed. Different sulphurated compounds are used as model in biodesulphurization processes, naphtothiophene (NTH), benzothiophene (BTH), alkylated BTH, dibenzothiophene (DBT), alkylated DBT and their transformation products has been reviewed. DBT is the most frequently employed.

The physicochemical properties of nanoparticles determine their interaction with living organisms. Four different cerium oxide nanoparticles, including commercial materials, were characterized and compared with a micron-sized ceria. The formation of aggregates as well as z-potential, surface area, and chemical composition were determined. The formation of primary particle aggregates was a slow process that led to different particle sizes depending on the composition of the medium. In this paper, we describe the toxicity of cerium oxide for the self-luminescent cyanobacterial recombinant strain Anabaena CPB4337 and the green alga Pseudokirchneriella subcapitata. The toxicity for Anabaena exposed to nanoparticles in pure water for 24 h ranged from 0.27 to 6.3 mg/l; P. subcapitata EC 50 (yielded effective concentration of nanoparticles that inhibits the cellular function of interest by 50%) values in the 2.4-29.6 mg/l range. Images of both organisms showed membrane disruption and highly damaged cells. Free cerium was highly toxic for both organisms, but the negligible amount found dissolved in the nanoparticle suspensions could not explain the observed toxic effect of nanoceria on the aquatic organisms; the dissolution of zinc could contribute to the toxicity of bulk material but could not explain the toxic effect of nanoceria either. We found no evidence of nanoparticle uptake by cells, but our observations suggested that their toxic mode of action required direct contact between nanoparticles and cells; in the case of the cyanobacterium, cells completely coated by layers of ceria nanoparticles were observed. Cell damage most probably took place by cell wall and membrane disruption; further research is needed to find out whether the oxidative activity of ceria could be responsible.